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C#,VB.NET从JSON数据里提取数组中的对象节点值

news 2025/7/4 7:50:26

在VB.NET中，若要从 JSON 数据里提取Data.DataList数组中的CategoryId，并将其转换为VB.NET数组，可借助Json.NET（Newtonsoft.Json）库来实现。下面为你详细介绍具体的实现步骤和代码示例：

一、实现 JSON 到数组的转换

方法 1：通过 JObject 解析（灵活通用）

Imports Newtonsoft.Json
Imports Newtonsoft.Json.LinqPublic Function ExtractCategoryIds(jsonText As String) As Long()Try' 解析JSON根对象Dim jsonObj As JObject = JObject.Parse(jsonText)' 获取DataList数组Dim dataList As JArray = jsonObj?("Data")?("DataList") as JArrayIf dataList Is Nothing ThenReturn New Long(-1) {}  ' 返回空数组End If' 提取CategoryId并转换为数组Return dataList.Select(Function(item) item?("CategoryId")?.Value(Of Long)()).Where(Function(id) id.HasValue).Select(Function(id) id.Value).ToArray()Catch ex As ExceptionConsole.WriteLine("JSON解析错误: " & ex.Message)Return New Long(-1) {}  ' 出错时返回空数组End Try
End Function

方法 2：反序列化为强类型对象（类型安全）

Imports Newtonsoft.Json' 定义数据模型
Public Class RootObjectPublic Property Code As IntegerPublic Property Data As DataObject
End ClassPublic Class DataObjectPublic Property TotalCount As IntegerPublic Property PageIndex As IntegerPublic Property PageSize As IntegerPublic Property DataList As List(Of CategoryItem)
End ClassPublic Class CategoryItemPublic Property CategoryId As Long
End Class' 转换方法
Public Function ExtractCategoryIdsWithModel(jsonText As String) As Long()Try' 反序列化为强类型对象Dim root As RootObject = JsonConvert.DeserializeObject(Of RootObject)(jsonText)' 提取CategoryId数组If root?.Data?.DataList Is Nothing ThenReturn New Long(-1) {}End IfReturn root.Data.DataList.Select(Function(item) item.CategoryId).ToArray()Catch ex As ExceptionConsole.WriteLine("JSON反序列化错误: " & ex.Message)Return New Long(-1) {}End Try
End Function

二、使用示例

Sub Main()Dim jsonText As String = "{""Code"":200,""Data"":{""TotalCount"":14,""PageIndex"":1,""PageSize"":100,""DataList"":[{""CategoryId"":271},{""CategoryId"":272}]}}"' 方法1：动态解析Dim categoryIds1 As Long() = ExtractCategoryIds(jsonText)' 方法2：强类型解析Dim categoryIds2 As Long() = ExtractCategoryIdsWithModel(jsonText)' 输出结果Console.WriteLine("提取的CategoryId数组:")For Each id In categoryIds1Console.WriteLine(id)  ' 输出: 271, 272Next
End Sub

三、关键要点说明

空值处理：
- 运用?.操作符来避免出现NullReferenceException。
- 对可能为空的数组进行检查，防止程序崩溃。
类型转换：
- 采用Value(Of Long)()方法将 JSON 值转换为 Long 类型。
- 借助Where(Function(id) id.HasValue)过滤掉无效的值。
异常处理：
- 捕获JsonReaderException和JsonSerializationException，增强程序的健壮性。
- 出错时返回空数组，而非Nothing，减少上层代码的判断逻辑。

四、扩展功能

1. 处理嵌套路径（通用方法）

Public Function ExtractValuesByPath(jsonText As String, path As String) As Long()TryDim jsonToken As JToken = JToken.Parse(jsonText)Dim tokens As IEnumerable(Of JToken) = jsonToken.SelectTokens(path)Return tokens.Select(Function(token) token.Value(Of Long)()).ToArray()Catch ex As ExceptionConsole.WriteLine($"提取路径 {path} 出错: {ex.Message}")Return New Long(-1) {}End Try
End Function' 使用示例
Dim categoryIds As Long() = ExtractValuesByPath(jsonText, "$.Data.DataList[*].CategoryId")

2. 异步解析大 JSON 文件

Public Async Function ExtractCategoryIdsAsync(jsonText As String) As Task(Of Long())TryUsing reader As New StringReader(jsonText)Using jsonReader As New JsonTextReader(reader)Dim serializer As JsonSerializer = New JsonSerializer()Dim root As RootObject = Await Task.Run(Function() serializer.Deserialize(Of RootObject)(jsonReader)End Function)Return root?.Data?.DataList?.Select(Function(item) item.CategoryId).ToArray() ?? New Long(-1) {}End UsingEnd UsingCatch ex As ExceptionConsole.WriteLine("异步解析错误: " & ex.Message)Return New Long(-1) {}End Try
End Function